In connectors for optical fibers for data transmission, ends of the respective optical fibers to be connected are inserted or terminated in ferrules brought into engagement with each other with the respective end surfaces of the optical surfaces contacting each other and in precise axial alignment.
As discussed in the parent application, a known technique for retaining the optical fiber securely in the ferrules employs the step of caulking the ferrules, in the radial direction, including the use of adhesives. However, disadvantages of this approach include difficulties in applying the correct amount of caulk and, therefore, the correct force, with the risk that the optical fiber is deformed and slips out of the ferrule easily, while performing the caulking by hand requires time consuming manipulation. Considerable time is also required to permit the adhesive to harden, resulting in poor productivity and quality control making this approach unsuitable for high volume mass production to meet minimal or zero defect quality standards.
In another approach taught by the parent application and disclosed in the priority Japanese patent application 3-167506, published on Jul. 7, 1991, the disadvantages associated with caulking are obviated by utilization of a ferrule assembly including an outer ferrule and an inner ferrule which clamps the optical fiber when is forced-fitted into the outer ferrule. An axially extending slit is formed through a wall of the inner ferrule to permit the inner ferrule to be deformed radially inwardly taking up the clearance provided by the presence of the slit and providing a compressive force which clamps the optical fiber tightly, retaining it in place in the assembly.
However, it has been found that there is a risk of an uneven clamping force being applied to the optical fiber clamped by the inner ferrule, resulting in instability of retention. In particular, when the inner ferrule is forced into the outer ferrule, there is a risk that opposed surfaces of the slits are brought into engagement with each other by deformation of the inner ferrule, precluding further inward deformation so that sufficient force for holding the optical fiber is then not obtained.